Originally Posted by DaFace
Did you mean to say you need the book? I don't see any reason to get a card for a cruise - especially since she wouldn't be able to use it for any other travel in the future.
The card is less expensive.
I agree it's better to just get the book but you only really "need" the card for the type of travel she will be doing. Even then she doesn't even need one, just bring a birth certificate + photo ID.